Contemporary hard disk drives include an actuator assembly pivoting through an actuator pivot to position one or more read-write heads, embedded in sliders, each over a rotating disk surface. The data stored on the rotating disk surface is typically arranged in concentric tracks. To access the data of a track, a servo controller first positions the read-write head by electrically stimulating the voice coil motor, which couples through the voice coil and an actuator arm to move a head gimbal assembly in lateral positioning the slider close to the track. Once the read-write head is close to the track, the servo controller typically enters an operational mode known herein as track following. It is during track following mode that the read-write head is used to access the data stored in the track.
Micro-actuators provide a second actuation stage for lateral positioning the read-write head during track following mode. They often use an electrostatic effect and/or a piezoelectric effect to rapidly make fine position changes. They have doubled the bandwidth of servo controllers and are believed essential for high capacity hard disk drives from hereon.
A central feature of the hard disk drive industry is its quest for greater data storage density, leading to continued reduction in track width, the flying height or vertical positioning of the read-write head off the rotating disk surface, and the size of the read head within the read-write head. As these factor shrink, the possibility of the read-write head contacting the rotating disk surface increases and the potential for damage to the disk surface and the read-write head grows. Thermal tip pole protrusion is a situation that can lead the read-write head into contact with the data of the rotating disk surface, particularly when in track following mode. This situation is usually caused by an excessive temperature near the read-write head of the slider.
Consider a heating element used as a vertical micro-actuator 98 embedded in a slider 90 to expand a deformation region 97 and reduce the vertical distance Vp between the slider and a rotating disk surface from an initial vertical distance to a reduced vertical distance as shown in FIG. 1A. Since when power is applied to the vertical micro-actuator, actuation of a deformation is always in the direction of decreased vertical distance. Though this approach is gaining favor at this time, typically complicated schemes should be incorporated eclectically with this device in order to avoid undesirable head to disk surface contacts due to excessive pole tip protrusion. Excessive overheating can happen due to either malfunction of electrical control or sudden change of environmental conditions, especially high temperature and altitude. What is needed is a mechanism and method keeping the deformation region from overheating, and at the same time minimizing the chances of undesirable head to disk surface contacts.